Inland Waters
ISSN: 2044-2041 (Print) 2044-205X (Online) Journal homepage: http://www.tandfonline.com/loi/tinw20
Carbon dioxide emissions from cascade hydropower reservoirs along the Wujiang River, China Shuang Li, Fushun Wang, Tao Zhou, Tianyu Cheng & Baoli Wang To cite this article: Shuang Li, Fushun Wang, Tao Zhou, Tianyu Cheng & Baoli Wang (2018): Carbon dioxide emissions from cascade hydropower reservoirs along the Wujiang River, China, Inland Waters, DOI: 10.1080/20442041.2018.1442040 To link to this article: https://doi.org/10.1080/20442041.2018.1442040
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Published online: 09 Apr 2018.
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Inland Waters, 2018 https://doi.org/10.1080/20442041.2018.1442040
Carbon dioxide emissions from cascade hydropower reservoirs along the Wujiang River, China Shuang Li,a Fushun Wang,a Tao Zhou,a Tianyu Cheng,a and Baoli Wangb a
School of Environmental and Chemical Engineering, Shanghai University, Shanghai, China; bInstitute of Surface-Earth System Science, Tianjin University, Tianjin, China
ARTICLE HISTORY
ABSTRACT
Currently, CO2 emissions from cascade hydropower reservoirs are not well understood. In this study, we investigated the seasonal carbon dioxide partial pressure (pCO2) and related environmental factors in 4 cascading reservoirs (Hong Jia Du, Dong Feng, Suo Feng Ying, and Wu Jiang Du) of Wujiang River, southwest China. The results showed that pCO2 in the surface water of these reservoirs had obvious spatiotemporal changes and generally decreased from the riverine zone to the lacustrine zone in each reservoir. In summer, pCO2 was highest downstream of the dam because of stratification and deep water discharge for hydropower generation, whereas pCO2 was much lower in the surface water of the lacustrine zone because of carbon removal by photosynthesis. When water temperature was low, however, pCO2 was higher in the surface water of the lacustrine zone because of respiration and organic decomposition. Among these reservoirs, only Suo Feng Ying had CO2 emissions higher than the average value of natural lakes. In addition, CO2 emission flux showed an exponentially negative relationship with hydraulic retention time of reservoirs, based on this work and other reports of reservoirs in the Yangtze River basin.
Introduction Hydropower reservoirs play an important role in supplying the demand for energy worldwide, especially in emerging nations (Demarty and Bastien 2011). Over the past decades, large numbers of dams have been built for the production of electricity, flood control, and water resource management (Bai et al. 2015). Hydroelectric power had been considered a good substitute for fossil fuels, which release a large amount of carbon dioxide (CO2) into atmosphere; however, investigations in tropical reservoirs indicated that hydroelectric dams might be a source of CO2 (Kelly and Hecky 1993, Fearnside 2002). Early estimates by St. Louis et al. (2000) suggested that 272.7 Tg yr−1 of C as CO2 and 52.5 Tg yr−1 of C as CH4 were released from the global hydropower reservoirs. Barros et al. (2011) further estimated that reservoirs released 48 Tg yr−1 of C as CO2 and 3 Tg yr−1 of C as CH4 into the atmosphere (Barros et al. 2011). According to recent estimates by Deemer et al. (2016), C in amounts of 36.8 Tg yr−1 as CO2 and 13.3 Tg yr−1 as CH4 are released into the atmosphere (Deemer et al. 2016). This large discrepancy may result from a paucity of data and different
KEYWORDS
cascade reservoirs; carbon dioxide emission; hydraulic retention time; Wujiang River basin
extrapolation approaches. Moreover, reservoirs included in the estimations were mostly from Northern Europe and the Americas, excluding data from Asia where a large number of reservoirs have been constructed and where more hydroelectric reservoirs are planned for the future (Li et al. 2015, Zarfl et al. 2015). Therefore, further estimates need more detailed information from reservoirs in different regions (Zhao et al. 2012). In addition, the estimate of CO2 emissions may be more complicated in cascade reservoirs than in single reservoirs. Previous studies were based on isolated reservoirs rather than a cascade of linked reservoirs on the same river. The CO2 released from one reservoir may not depend on the state of that reservoir alone, but also on conditions in upstream reservoirs because of the joint operation in a cascade reservoir system. In this study, we investigated 4 large hydroelectric reservoirs in a cascade on the Wujiang River, southwest China. The main objectives of this study were to (1) elucidate the spatiotemporal changes of pCO2 and CO2 emissions in a typical cascade reservoir system, and (2) to assess the impact of hydraulic retention time (HRT) on CO2 emissions.
CONTACT Fushun Wang
[email protected]; Baoli Wang
[email protected] The Supplementary material for this article can be accessed here at https://doi.org/10.1080/20442041.2018.1442040 © 2018 International Society of Limnology (SIL)
Received 28 July 2017 Accepted 6 February 2018
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S. LI ET AL.
Figure 1. Distribution diagram of sampling locations: Hong Jia Du (HJD), Dong Feng (DF), Suo Feng Ying (SFY), and Wu Jiang Du (WJD) reservoirs.
Methods Study area The Wujiang River (26°07′~30°22′N, 104°18′~109°22′E) is a classic canyon river, mainly flowing through a karst landscape in Guizhou Province, southwest China (Fig. 1). Approximately 87% of the basin comprises plateaus and mountains. The annual average temperature is 14 °C,
and the annual average rainfall is 1195 mm, occurring mostly in summer and spring (Yao et al. 2011). The study reservoirs, Hong Jia Du (HJD), Dong Feng (DF), Suo Feng Ying (SFY), and Wu Jiang Du (WJD), are all located on the upstream part of the Wujiang River at an elevation between 1140 m (HJD) and 760 m (WJD; see Table 1 for basic characteristics of these reservoirs).
INLAND WATERS
Table 1. The basic characteristics of the study reservoirs: Hong Jia Du (HJD), Dong Feng (DF), Suo Feng Ying (SFY), and Wu Jiang Du (WJD). Unit Regulation mode Year of construction Total water volume Maximum depth Mean depth Drainage area Average annual flow Average retention time
108 m3 m m km2 m3 s−1
HJD Multi-year 2004 49.5 130 60 9900 155
DF Seasonal 1995 10.3 76 25 18 161 343
SFY Daily 2005 2.0 80 21 21 862 427
WJD Seasonal 1983 23.0 95 33 27 790 502
d
369
28
4
49
Sampling Water samples were collected quarterly from October 2015 to July 2016. Sample points included W1, W6, S1, and M1 on the rivers flowing into the reservoirs (HJD, DF, DF and SFY, respectively; Fig. 1). Site M1 is downstream of the Hongyan dam, sites W2–W4, W7–W9, W11, and W13–W15 are within the reservoir, and sites W5, W10, W12, and W16 are downstream of the dam. Water samples were collected at 6 depths (0, 5, 10, 20, 40, and 60 m) with a Niskin bottle at sites W4, W9, and W15. Water was collected only at the surface of SFY Reservoir because it had the characteristic of a river and was considered not stratified (Zhao et al. 2013). Water temperature, pH, and dissolved oxygen (DO) were measured in situ with a YSI-6600v2 meter (YSI, USA). The concentration of total chlorophyll (Chl) was measured on the spot with a pulse-amplitude-modulated fluorimeter (Phyto-PAM, Walz, Effeltrich, Germany). Light intensity of MF32 (measured frequency 32: the most suitable frequency to measure Chl concentration) was 16 μmol m−2 s−1, detection limit of Chl was 0.01 μg L−1, and alkalinity was titrated with HCl in situ (Wang et al. 2011, Peng et al. 2013). Samples filtered through 0.45 μm filters were used to analyze major cations and anions. Samples for cation analysis were acidified to pH
